1. Field of the Invention
The invention relates generally to electrical power switchgear with motor operators and, more particularly, to motor operators for power switches with a drive system that facilitates switch operation by force other than from the motor of the operator, such as manually applied force, even for switches at overhead (or pole-top) locations.
2. Background Art
Motor operators are widely used in combination with power switches. A variety of operators are in use with various features to permit a switch operation to be performed manually. These have included operators with features for mechanically decoupling the operator's drive system from the motor. Decoupling has taken a number of different forms.
Power switches are applied at a variety of locations including some at surface, or ground level, locations relatively easily accessed for manual decoupling and switch operation and some at overhead (or pole-top) locations less easily accessed.
For example, some overhead switches have a motor operator at or near ground level with a mechanical (reciprocating or torsional) link to a switch drive at the overhead location that may be forty or fifty feet higher. Such an operator is, for example, described in Cleaveland/Price Inc., Bulletin DB-128C01 of 2001. The motor operator is housed in an enclosure also containing other power, control and protection elements, including elements for initiating operation from a remote control station. To perform a manual switch operation with that system, a worker removes a hand tool (e.g., a hand crank) from the enclosure whose removal opens a handle interlock switch that in turn opens the motor control circuit so the motor will not operate during manual operation. A decoupler pin, or other mechanical release element, is available for manual removal so a manual switch operation can be performed using the hand tool to apply force to move the mechanical linkage to the overhead switch without requiring manual turning of the motor. When manual operations are completed, replacement of the hand tool and the decoupler pin restores the system for operation by the motor.
Such systems have been quite successful. Recently, however, some interest has developed in equipping overhead switches with motor operators at the pole-top location with only a short mechanical link to the switch. This can, for example, lessen any concerns about dimensional variance of the mechanical linkage over the long life of an installation, minimize ground equipment subject to safety or vandalism concerns, and provide an overall cleaner, uncluttered look to an installation (even though some power supply and control elements can be housed at a surface location, preferably of course well secured in a locked enclosure). While such operators may be similar to the former ground-based units in some respects, e.g., including remotely initiated power operation, if the same features for manual operation are retained there is the problem of accessing the manual elements, such as requiring a worker to climb up to the operator, or use of a lift-truck, which is expensive and troublesome.
Among other prior art of switch motor operators with some kind of decoupling for manual operation, whether or not for overhead installations, are those contained in the following U.S. patents (which are merely partially and briefly described).
Evans U.S. Pat. No. 3,980,977, Sep. 14, 1976, illustrates a system in which insertion of a specified hand tool at a particular location of a clutch mechanism in a motor operator disconnects the motor from the mechanism and allows manual rotation of a drive lever that recharges a wound spring operating mechanism.
Ramos et al. U.S. Pat. No. 5,091,616, Feb. 25, 1992, shows a pole-top motor operator and specially designed switch combination with a disconnect linkage manually operable by a hook stick or the like that moves switch-pole housings of the switch.
Sanders U.S. Pat. No. 5,856,642, Jan. 5, 1999, discloses an infinite engagement friction clutch coupled switch operator with selectable engagement and disengagement by a user to allow for manual operation.
Lo et al. U.S. Pat. No. 5,895,987, Apr. 20, 1999, and U.S. Pat. No. 6,025,657, Feb. 15, 2000, present a switchgear motor operator with a drive including a clutch with a hub and friction discs or an actuator-follower arrangement with opposing actuating and follower surfaces that is subject to an automated control means that responds to a switch operation to reverse the engaging elements to allow manual operation.
Such known art, however useful each may be and with whatever varied tradeoffs each carries with it in terms of high or low cost, convenience, complexity, and susceptibility to inoperability due to a loss of power or functionality, all has a common characteristic in that each necessitates performing an explicit decoupling process, in addition to the merely normal switch opening and closing of a motor operator, either manually or motor driven and either specifically initiated when desired or automatically by a control system.